This invention relates to a process for de-inking printed fibrous materials to produce a high quality stock. In particular, this invention is directed to a de-inking process for printed paper that utilizes an aqueous, de-inking solution containing a mixture of nonionic surfactants and produces a paper stock of high quality.
Paper manufacture does not unduly damage or alter the character of the essential fibers from which paper is made, therefore such fibers may be recovered from used or waste paper and reused for the manufacture of new paper stock. From a practical standpoint, the principal criterion that determines the commercial value and acceptability of a particular de-inking process is the capacity to economically upgrade printed paper stock to the quality and color of the original paper stock. Important factors in determining the quality of the upgraded paper stock are the brightness and/or the whiteness of the paper stock. These factors are improved by the de-inking process of this invention.
Many processes for de-inking waste paper utilizing aqueous solutions containing surfactants, usually in the presence of phosphate-type water softening agents, are known in the art, and have been used to recover fibers from printed paper for subsequent reuse. These processes are undesirable from an ecological standpoint because of the presence of the phosphates and are generally expensive because the de-inking operation usually is carried out at elevated temperatures. Furthermore, the paper pulp derived therefrom is not of sufficient brightness to be used for the manufacture of high quality paper stock. Illustrative proposed prior art processes for waste paper de-inking are disclosed in U.S. Pats. No. 3,056,713 to Gaertner, No. 3,069,308 to Lissant, No. 3,098,784 to Gorman, Jr., No. 3,354,026 to Illingworth, No. 3,354,028 to Illingworth et al., No. 3,392,083 to Illingworth, No. 3,446,696 to Illingworth, No. 3,501,373 to Illingworth, No. 3,808,089 to Von Koeppen et al., No. 3,932,206 to Illingworth et al. and in French Pat. No. 1,453,204. Another illustrative prior art process is disclosed in British Pat. No. 1,347,971 according to which paper to be de-inked is first impregnated with an oil-soluble, substantially water-insoluble surfactant, then pulped in an aqueous alkaline medium, and subsequently recovered therefrom. However, none of these prior art processes suggests the use of an aqueous, phosphate-free de-inking solution which contains a mixture of water-soluble and oil-soluble nonionic surfactants having certain properties, and which is capable of effective de-inking even at about room temperature and at relatively low surfactant concentration in the solution. These features are of considerable significance in that a relatively inexpensive and ecologically compatible de-inking process is provided.